1. Field of the Invention
This invention relates to the electric lamp art and has particular reference to an improved amalgam-containing low-pressure discharge lamp, such as a fluorescent lamp.
2. Description of the Prior Art
Fluorescent lamps that contain a suitable metal, such as indium or the like, which combines with the mercury dosed into the lamp to form an amalgam that controls the pressure of the mercury vapor during lamp operation are well known in the art. Fluorescent lamps having a disc-shaped body of amalgamative metal which is attached to the inner surface of the bulb between the electrodes are disclosed in U.S. Pat. Nos. 3,152,278 and 3,351,797. Another fluorescent lamp design that is provided with a circumferential band of indium-mercury amalgam which is disposed on the inner surface of the bulb midway between the electrodes is disclosed in U.S. Pat. No. 3,392,298. According to another concept indium, in the form of a powder, is admixed with the phosphor particles that are coated onto the inner surface of a fluorescent lamp envelope (U.S. Pat. No. 3,339,100).
A more recent trend in the evolution of amalgam-type fluorescent lamps is to place tha amalgamative metal on the glass stems that are sealed into the ends of the bulb. A fluorescent lamp having a stem component that is provided with a thin layer of amalgam-forming metal which is sprayed onto the flared skirt portion of the glass stem is disclosed in U.S. Pat. No. 3,548,241. A fluorescent lamp having a thin sleeve of amalgamative metal that is held in encircling relationship with the tubular part of the stem by a wire-mesh collar assembly is described in U.S. Pat. No. 3,619,697 issued to G. S. Evans, one of the joint authors of the present invention. In other recently developed and known amalgam-fluorescent lamps the amalgamative metal is deposited on an anode or a shield structure that is associated with the cathode, or it is placed within the tipped-off exhaust tubulation of one of the stems.
In the improved amalgam-type fluorescent lamps disclosed and claimed in the aforementioned pending applications Ser. Nos. 293,239 and 473,959 of Chalmers Morehead, the amalgamative metal is divided into a plurality of discrete bodies or bits that are attached directly to the vitreous stem before the latter is sealed to the rim of the envelope. Such attachment is achieved by heating the stem and pressing the metal bits against the hot surface of the stem to fuse the bits to the glass, or the metal bits are disposed in recesses that are molded into the stem surface. When metal bits of large size and mass are employed, a layer of inert material that is porous to mercury vapor is applied over the bits and attached to the surrounding portions of the stem to prevent the heat-softened or melted bits from falling off the stem during the sealing-in operation. A porous matrix of fused admixed material can also be used as an auxiliary retaining means.